Implications of bycatch reduction strategies for the economic viability of mixed fisheries

International audienceThere is growing recognition worldwide that the impacts of fishing on non-targeted components of marine ecosystems should be included in the assessment of fisheries sustainability. This leads to the inclusion of new constraints in evaluations of the long-term bio-economic performance of fisheries. In this paper, we analyze the implications of such constraints based on the case of bycatch of juvenile hake in the Bay of Biscay (ICES area VIIIa,b) trawl fishery for nephrops. The analysis is based on a discrete time model of the trawl fishery including an age-structured representation of stock dynamics, with uncertainty. We define sustainability using the viability framework of analysis: viability objectives are represented as constraints which relate to the economic status of the fishing fleet and to the biological status of fish stocks. We include an ecological constraint defined as a minimal target threshold for the recruitment of mature hakes, which is related to the fishing mortality induced by trawlers on juvenile hake. Based on stochastic analysis, we define the probability that both economic and ecosystemic constraints are met, as a function of the level of these constraints. We use the model to assess the sustainability of the fishery under different scenarios as regards bycatch reduction strategies. Keywords: Sustainable fish eries, management procedures, stochastic viabilit